Depyrogenation is a cleaning process in which fever-causing bacterial carcasses, or other materials, pyrogens, are oxidized to remove them from the surfaces of objects such as glassware. Depyrogenation is commonly performed on materials prior to their introduction to an environment having a precisely controlled particle density such as a clean room, a laboratory, or a production area.
In order to depyrogenate many objects, the objects are heated to approximately 230.degree.-270.degree. C. in a clean room environment, i.e., an environment having a precisely controlled particle density in its atmosphere. Desired particle densities may be obtained by passing air through specialized filters (e.g., HEPA filters) of various sizes to filter out particulate matter above given size ranges. However, if air travelling through a filter changes in temperature at a rate of about 2.degree. C. per minute or more, the resulting thermal shock or stressing of the filter may cause the filter itself to emit particulate matter into the air. The quantity of particulate matter emitted varies with the rate of temperature change of the air provided to the filter.
In the past, it has generally been necessary to heat the air supplied to a depyrogenation oven at a rate of not greater than about 2.degree. C. per minute to avoid thermal stress to in-line filters. A heating rate of less than 2.degree. C. per minute can require a heating time of approximately two hours to reach a suitable depyrogenation temperature. Long heating and cooling times substantially reduce the output of a depyrogenation oven.
It would be desirable to provide a depyrogenation oven that can be heated quickly with filtered air to a desired depyrogenation operating temperature without causing emission of particulate material from a filter due to thermal stress.